Electrical cable

ABSTRACT

An electrical conducting cable for submersible motors adapted for use in high temperature, high pressure mineral wells. The cable includes separately insulated conductors disposed within an epichlorohydrin rubber jacket. The conductors are insulated with a layer of heat stabilized ethylene propylene rubber as the primary insulation. The jacketed cable unit is protected by an outer armor formed of a high temperature, high molecular weight, heat stabilized, polypropylene. The cable thus formed is flexible, abrasion resistant, solvent resistant, liquid impervious, heat insensitive and unaffected by well environment.

[111 3,710,009 [451 Jan.9,1973` United States Patent [191 Hoeg et al.

3,614,300 l0/l97l Wilson..............................174/1IOR [54] ELECTRICAL CABLE [75] Inventors: Donald F. Hoeg Mt. Prospect, Ill.;

Leo V. Le, Tlilsa, Okla.; Donatas Pnmary ExafmfrTE' A' Goldberg Tunnel, Buffalo Grove, mI Attorney-William S. McCurry et al. [73] Assignee: Borg-Warner Corporation, Chic [57] ABSTRACT ago,

References Cited unaffected by well environment.

UNITED STATES PATENTS 6 Claims, 2 Drawing Figures 3,299,202 Brown l0 R 17 (co/vou: rom

15 ipv4 YPROP n sA/E) ELECTRICAL CABLE BACKGROUND OF THE INVENTION This invention relates to electrical cable. More particularly, it relates to electrical cable utilized to deliver electrical energy to submersible motors adapted for use in high temperature, high pressure mineral wells.

Submersible pumps used in oil, mineral and water wells normally include a prime mover in the form of an electric motor directly coupled to the pump and disposed deep within the well. lt is, therefore, necessary to provide an electrical connection between the motor and a source of electrical energy at the surface. This is normally accomplished by the use of an electrical conducting cable which extends between the source of electrical energy and the motor.

In many instances, the motors operate at relatively high power levels, in some cases exceeding 200 horsepower. Normally, the motors used are of the threephase type and the associated cable includes three separate electrical conductors.

The electrical cable must have adequate current carrying capability and must be of sufficient dielectric strength to prevent electrical losses even under the adverse environmental conditions usually found within vthe well. The environmental conditions of the well vary generally depending upon. geographical location. In some cases, the well fluid is highly corrosive and, in many instances, well temperatures exceed 0F. Many mineral wells contain dissolved H,S gas, carbonates, salts and traces of oil. Additionally, the wells are quite deep, averaging 4,000 to 10,000 feet. The electrical cable must possess enough physical strength to allow insertion of the motor and cable to these depths and the outer surface of the cable must resist the abrasion associated with insertion. Since the cable is normally wound upon storage or transportation reels, it must possess the additional property of flexibility so that it will resist physical damage caused by reeling.

Typical cable construction presently being utilized includes three conductors of stranded copper separately insulated and helically wound to form a single unit. The stranded conductors are insulated with a material of high dielectric strength such as polyethylene or polypropylene. The helically wound and insulated conductors are sheathed` in an extruded jacket of nitrile rubber surrounding the insulated conductors.

One common form of jacketed cable is covered with an outer armor in the form of a continuous wrapped band of metallic material. This band is lapped as it is wound. The armor provides abrasion resistance. Usually, the armor is formed of steel or bronze; however, in many special applications, such as wells which are excessively corrosive, stainless steel or exotic metals such as monel metal must be used.

The equipment required to wind the metallic band to form the armor is expensive, complex and slow. Further, splicing of the armor cable in the field is complicated because of the presence of the metallic outer layer.

Polyethylene has also been employed to a limited extent as the outer armor, but it has been found that the same does not stand up under severely high temperatures.

Proper material selection for the cable armor has always presented difficulties. Many different armor materials must be utilized depending upon the well conditions and no single cable construction has been found suitable for universal application. This is especially true for the deep, high pressure and high temperature wells.

Electrical power cables constructed as previously described which have been used in high temperature, high pressure mineral wells, fail because of temperature distortion of the thermoplastic cable components, corrosion of the armor, or chemical and solvent attack of the elastomer jacket. Since most mineral wells contain dissolved HBS gas, carbonates, water, salts and traces of oil, no single material has the resistance to solvents, heat and pressure to operate for prolonged periods in such an environment.

An additional problem encountered by cables in such an environment is deformation under load. The cables arev subject to both compressive and tensile forces and, under high temperatures, there is a marked tendency for the jacketing to deform resulting in dislocation ofthe conductors and phase to phase or phase to ground short circuitry.

Rupture of the armor due to swell of the jacket is another example of deformation which occurs in such an environment. Rupture of the total construction also occurs during retraction of the Cable from the well as a result of the depressurization of fluids which have permeated the cable.

These and other associated difficulties have clearly dictated the need for an improved, impermeable, environment insensitive cable construction.

Accordingly, it is the principal object of the present invention to provide an improved multicomponent cable construction for a submersible motor.

More particularly, it is an object of the present invention to provide a cable for a submersible motor designed for service under high temperature, high pressure mineral well conditions in which oil content is a minor component.

SUMMARY OF THE INVENTION The present invention relates to an improved multicomponent electrical cable for submersible motors adapted for use in high temperature, high pressure mineral wells. More particularly, it relates to a cable construction which includes an outer armor of high temperature, high molecular weight, heat stabilized polypropylene, an inner jacket of epichlorohydrin rubber and a high temperature, synthetic, organic insulator surrounding the electrical conductors.

The polypropylene used for the outer armor is of a type not normally used for wire insulation because of its processing difficulties but possesses a maximum in heat resistance especially with respect to high temperature creep characteristics. An example of a suitable armor material is a high molecular weight polypropylene homopolymer of high isotactic level.

The epichlorohydrin rubber used for the jacket is compounded for the minimum of oil and water permeability and swell to prevent deformation.

The type of high temperature, synthetic, organic insulator disclosed for use in high temperature, high pressure mineral wells is an olefin rubber such as, for example, one of the class of ethylene propylene copolymer rubbers and the ethylene propylene non-conjugated diene terpolymer rubbers. Such rubbers are excellent electrical insulators at elevated temperatures when not in direct contact with oil.

The outer armor of polypropylene is water insensitive and water impermeable so that it protects the epichlorohydrin rubber jacket. The epichlorohydrin rubber jacket is insensitive to any oil which may have permeated the polypropylene armor and in addition is highly oil impermeable providing a barrier which protects the olefin rubber insulation. The result is a minimum of water or oil permeation, or any effect therefrom.

These and other objects and advantages of the present invention will become apparent with reference to the following description and accompanying drawings.

DESCRIPTION OF DRAWINGS FIG. l is a fragmentary perspective view of a section of electrical conducting cable for submersible motors illustrating various features of the invention.

FIG. 2 is a cross-sectional view of the cable of FIG. l taken generally along the lines 2-2 of FIG. l.

DESCRIPTION OF ILLUSTRATED EMBODIMENTS Referring now to the drawing, there is shown a multicomponent electrical conducting cable for a submersible motor designed for use in high temperature, high pressure mineral wells which is illustrative of the principles ofthe present invention.

FIG. l shows a cable section which includes conductors ll, a resilient jacket 13 and an outer armor l5.

Each conductor ll is formed of stranded wire 17 helically wound to prevent separation of strands. These separate strands may be tinned to minimize chemical interaction between the conductor and the insulating material.

In the illustrated embodiment each conductor includes seven strands. The number of conductors, the diameter of the conductor and number of wires is, of course, dependent upon the load carrying capabilities required for a particular cable application. It should additionally be noted that any suitable conducting material may be used, such as for example, copper, aluminum, etc.

Each wound set of wire strands forms a single conductor and is separately insulated by an insulation layer 19. The conductor insulation 19 is formed of a high temperature, organic, synthetic material of high dielectric strength. One class of materials found to be satisfactory for this purpose are the olefin rubbers and in particular the ethylene propylene copolymer rubbers and the ethylene propylene non-conjugated diene terpolymer rubbers.

lf the conducting material is copper the ethylene propylene rubber conductor will have to be copper stabilized in addition to being heat stabilized. Copper sta bilization of olefin rubbers is well-known in the art and can be accomplished in a manner such as disclosed in U. S. Pat. Nos. 3,535,257 or 3,549,572 or any other acceptable method of copper stabilization. If the con- A preferred embodiment of a heat stabilized ethylene propylene rubber insulating material is described in U. S. Pat. No. 2,933,480.

As previously mentioned this ethylene propylene rubber may have to be modified for copper or other metal stabilization depending upon the conductive material.

The wound conductor unit is disposed within the jacket 13 which is comprised of a high molecular weight epichlorohydrin rubber compounded for the minimum of oil and water permeability and swell. This jacket may be extruded about the wound conductors and preferably is formed to ll interstices 23 between adjacent conductors.

One preferred embodiment is a formulation of epichlorohydrin compounded of the materials and in approximately the ratios as follows:

Pans/100 Parts Trade Name Material of Rubber Available From Herclor H high molecular wt. 100.0 Hercules, lnc.

epichlorohydrin rubber Span 60 surface active agent 1.5 Atlas Chemical comprised of partial Industries esters of hexitol anhydrides di-basic Dyphos XL lead phosphite 10.0 National Lead (heat stabilizer) Company N B C nickel dibutyl 1.0 Du Pont dithiocarbamate (anti-oxidant) Cumate copper dimethyl 0.125 R. T. Vanderbilt dithiocarbamate (accelerator) Company Phenothiazine phenothiazine 1.0 Fisher Scientific Company Vulcan carbon black 30.0 Cabot Corporation (filler) Hi Sil 23 3 silica (filler) l0.0 P.P.G. Industries TE- plasticizers 0.5 Technical Processing, c. TP- plasticizers 1.0 Thiokol Chemical Corp. Azelaic Acid dispersant 4.0 Eastman Organic Chemicals NA-22 2 mercaptothiazoline 1.0 Du Pont (accelerator) The extruded epichlorohydrin jacket completely fills the voids formed about the separately insulated conductors. This precludes exposure of the insulation to well fluid and further prevents flow of well fluid along the cable length in the event that a rupture occurs at some point along the outer armor l5 and the outer periphery of jacket 13.

The jacket 13 of the cable is surrounded by the extruded outer armor l5 formed of a high temperature, high molecular weight, heat stabilized polypropylene.

A preferred embodiment of a high temperature, high molecular weight, heat stabilized polypropylene homopolymer is commercially available under the trade name Avisun 1046 from Amoco Corporation. This material has been found to possess the following physical properties.

Molecular Weight High as evidenced by reduced viscosity of nm, 3.5 dl/g tested in Decalin at C.

Specific gravity 0.090 0.91 at 23C (ASTM-D-7 Flow Rate at 230C, 2,160 gram load, 5.0 grams per l0 minutes (ASTM-D-l238-65T) Deflection temperature 230F at 66 PSI (ASTM-D-648-6l Deformation under load 3.5 percent at 2,000 PSI (24 hrs, at SOC) (ASTM-D-62l-64) Water Absorption 0.01 percent (ASTM-D-570 Flexural Modulus 180,000 PSI (0.05 in/min CHS) (ASTM-D-790-66) The polypropylene used for the outer armor must have a very low water sensitivity to protect the epichlorohydrin jacket from any swelling which, in turn, would keep any traces of oil from attacking the primary insulation. This is necessary because when unaffected by oil ethylene propylene rubber is an excellent electrical insulator at the elevated temperatures at which it must operate in a high temperature, high pressure mineral well.

The outer armor is preferably formed by extruding. The extruded armor is formed in surrounding relation to the jacketed cable unit as the cable unit progresses through an appropriate extrusion die. Thus, a completely sealed, fluid impervious armor is efficiently formed about the jacket 13 which separates the jacket and the well fluid and protects the internal components ofthe cable from physical and chemical damage.

The particular polypropylene described has a dielectric strength of about 600 to 750 volts per mil. It has excellent abrasion resistance and forms a smooth outer cable surface. It is resistant to the attack of chemical agents such as HZS gas, carbonates and salts and traces of oil which may be found within the well and provides a barrier against moisture, oils and greases. lt has a water absorption of about 0.03 percent. Additionally, this polypropylene retains its abrasion resistance at high temperatures and it has little, if any, environmental stress cracking. The polypropylene described is sufficiently resilient to allow reeling and unreeling of the motor cable without cracking the protective armor,

While polypropylene generally is somewhat sensitive to light and, under certain conditions, suffers loss of dielectric strength, it has been found that the addition of darkening pigments as well as ultra-violet light stabilizers to the polypropylene armor adequately protects the armor from deterioration caused by exposure to light.

Use of multicomponent cable such as that described provides a cable construction which is abrasion resistant, impervious to well fluids, flexible and unaffected by corrosive well environments arid high temperatures. Further, construction of the cable is simplified by extruding the armor onto the jacketed cable unit.

An example of a well cable illustrating features of the present invention has been constructed. It includes 3 seven-wire stranded copper conductors, each of which is surrounded by a heat and copper stabilized ethylene propylene rubber insulation having an average thickness of 0.072 inch. The separate conductors are durable conducting unit for use in the adverse environment associated with high temperature, high pressure mineral wells. The outer armor is easily formed and possesses the desirable physical properties making it suitable for application as a cable for submersible well motors.

While the epichlorohydrin rubber utilized for the jacket 13 was Herclor H (Hercules, Inc.), an epichlorohydrin homopolymer (poly (alpha-chloropropylene oxide)), other homopolymers of epichlorohydrin such as Hydrin (B.F. Goodrich) are suitable for this application. Also epichlorohydrin rubbers prepared from epichlorohydrin and ethylene oxide are suitable for the jacket 13. These copolymers are sold under the trade names Herclor C (Hercules, Inc.) and Hydrin 200 (B.F. Goodrich).

Various features of the invention have been particularly shown and described in connection with the illustrated embodiments of the invention. However, it must be understood that these particular arrangements are for illustrative purposes and that the invention is to be given its fullest interpretation within the scope of the appended claims.

What is claimed is:

1. A multicomponent electrical cable adapted for use with a submersible motor comprising at least one electrical conductor; a layer of insulating material surrounding said conductor formed of an olefin rubber; a resilient jacket surrounding said insulator comprising an epichlorohydrin rubber of high molecular weight and an outer armor surrounding said resilient jacket formed of a high temperature, high molecular weight, heat stabilized polypropylene.

2. A multicomponent cable as in claim 1 wherein said olefin rubber is an ethylene propylene copolymer rubber.

3. A multicomponent cable as in claim l wherein said olefin rubber is heat stabilized.

4. A multicomponent cable as in claim l wherein said olefin rubber is copper stabilized.

5. A multicomponent cable as in claim l wherein said olefin rubber is both heat Stabilized and copper stabilized.

6. A multicomponent cable as in claim l wherein said olefin rubber is an ethylene propylene non-conjugated diene terpolymer rubber.

Il: t 

2. A multicomponent cable as in claim 1 wherein said olefin rubber is an ethylene propylene copolymer rubber.
 3. A multicomponent cable as in claim 1 wherein said olefin rubber is heat stabilized.
 4. A multicomponent cable as in claim 1 wherein said olefin rubber is copper stabilized.
 5. A multicomponent cable as in claim 1 wherein said olefin rubber is both heat stabilized and copper stabilized.
 6. A multicomponent cable as in claim 1 wherein said olefin rubber is an ethylene propylene non-conjugated diene terpolymer rubber. 